The purpose of this project is to investigate the roles of pigmented cells in the maintenance of functional photoreceptor cells. Using ultrastructural histochemistry, microperoxisomes which contain catalase were found to be unusually abundant in the retinal pigment epithelium. The number of microperoxisomes increased three-fold in mice treated with hypolipidemic drugs to decrease their serum cholesterol and triglyceride levels. Both microperoxisomes and lipid droplets increased significantly following retinal damage by light. Microperoxisomes of the retinal pigment epithelium may be important in the storage and rapid turnover of lipids required for maintenance of photoreceptor outer segment membranes. Light was used to stimulate phagocytosis of shed outer segment membranes, and the steps in their intracellular digestion were examined in a mutant with a lysosomal defect like that found in the Chediak-Higashi syndrome. We have begun to apply the information gained to studies on the role of the retinal pigment epithelium in recovery from retinal damage by light.